Method for forming heat exchange element



March 18, 1969 RHODES ET AL 3,433,044

METHOD FOR FORMING HEAT EXCHANGE ELEMENT Sheet Original Filed Feb. 19, 1963 fUGf/Vf f. R/VUfifS AL V//\/ M KURZ INVENTOR.

ATTORNEYS March 18, 1969 E. E. RHODES ET AL 3,433,044

METHOD FOR FORMING HEAT EXCHANGE ELEMENT Sheet 2 of 5 Original Filed Feb. 19. 1963 INVENTOR.

ATTORNEYS March 18, 1969 RHODES ET AL 3,433,044

METHOD FOR FORMING HEAT EXCHANGE ELEMENT Sheet Original Filed Feb. 19. 1965 i.l Qww QQ mmw m w 6% a! K 9% b6 AL V/A/M/fi/AZ INVENTOR. ygggA m 50657175 5. xe/mzws United States Patent 3,433,044 METHOD FOR FORMING HEAT EXCHANGE ELEMENT Eugene E. Rhodes, Belleville, and Alvin M. Kurz, Oak

Park, Mich., assignors to Ford Motor Company, Dearborn, Mich., a corporation of Delaware Application Apr. 2, 1965, Ser. No. 445,073, now Patent No. 3,250,323, dated May 10, 1966, which is a division of application Ser. No. 259,547, Feb. 19, 1963, now Patent No. 3,214,954, dated Nov. 2, 1965. Divided and this application Dec. 30, 1965, Ser. No. 517,778 U.S. Cl. 72-186 4 Claims Int. Cl. B21d 13/00, 31/02, 53/00 ABSTRACT OF THE DISCLOSURE A method of manufacturing a heat exchange element from a strip of sheet metal wherein such strip is passed between a first roll die and a second roll die and in so passing is simultaneously corrugated, slitted and deformed characterized by providing on opposite sides of said strip during slitting and deformation opposing line pressures extending transversely in relation to such strip.

This is a division of application Ser. No. 445,073, now U.S. Patent 3,250,325, filed Apr. 2, 1965, which in turn is a division of application Ser. No. 259,547, now U.S. Patent 3,214,954, filed Feb. 19, 1963. The disclosures of these applications are incorporated herein by reference.

This invention relates to a method for simultaneous cutting, forming and shaping of repeated designs on sheet metal. In particular, this invention relates to a method for the manufacture of novel heat exchange fin structures or spacer strips for use in a device wherein heat exchange is effected between a liquid and a gas, as, for example, in automobile radiators and heaters. The fin structure here employed to illustrate the method of manufacture is especially adapted for use as a part of the main cooling system of an engine and will be so referred to hereinafter for the purpose of disclosing the novel features and advantages of such method.

Although details of construction may vary, an engine cooling radiator ordinarily includes an inlet tank and an outlet tank for suitable connection with the water jacket of the engine, and a core or heat dissipating unit interposed between the two tanks for the travel of water in thin streams from one tank to the other through a number of spaced passageways or water tubes of suitable heat exchange material. Between each pair of these water conduits flows an air stream to take up or absorb heat carried by the water. A heat exchange fin structure and spacer element comprising a thin strip of a suitable metal or alloy, e.g. copper, brass, etc., is generally folded back and forth and interposed between the Water tubes for cooperation therewith to divide the intervening space into a number of small air cells.

In this type of spacer strip the portion extending between folds or major corrugations will herein be referred to as the heat exchange fin, the fin proper or merely the fin.

It was early recognized that more etficient use could be made of the air flow between the water tubes if a greater proportion of the air stream is brought into direct contact with the metal of the spacer strip and/or the walls of the water tubes. This led to the incorporation of transverse serpentine corrugations to provide an undulating flow in the air passage through the individual cells. In other designs, openings have been provided in the fin proper to allow air to flow from one cell into another in its passage through the core. In modifications of this design, louvers have been employed adjacent to such openings to divert air through such openings.

The louvered fins heretofore employed exhibit certain undesirable characteristics. Some of these are inadequacies of the basic design while others result from the methods and tools employed to form the intended design.

Design weaknesses include improper positioning, alignment and shaping of the louvers employed. This can reduce the efliciency of the entire cooling system by misdirecting or failing to direct the air flow. Maximizing the cooling efficiency of the core results from maximizing the wiping contact of the air on metal without undue impedance or resistance to flow. Too often in the past the value of laminar flow either has been overlooked or rejected in a misguided search for designs adapted to maximize turbulence. Furthermore, methods heretofore employed to form the design on the fin strip have resulted in uneven fin surfaces which impair the efficiency of the soldering process whereby the fin is made fast to the adjacent water tubes. This results in both inadequate connections and the plugging of air passages.

It is one object of this invention to provide an improved fin structure for use in a heat exchange device as hereinbefore described which will increase the heat absorption of an air stream passing through such device while reducing obstructions to such flow which do not contribute to heat exchange efiiciency.

It is another object of this invention to provide an improved fin structure that will reduce losses in heat exchange efiiciency that result from prolonged contact between air and the metal of such devices after a practical level of heat absorption has been reached.

Many other objects and advantages of this invention will be obvious to those skilled in the art from the disclosure herein given.

In the drawings, wherein like reference characters indicate like or corresponding parts:

FIGURE 1 is a partially completed front view of an automobile radiator illustrating one use of the spacer strips or fins structures of this invention;

FIGURE 2 is a perspective view of a fin strip of this invention with portions thereof shown in the folded and unfolded state to illustrate the relationship of adj acent fins in the spacer strips of this invention;

FIGURE 3 is a schematic view of two fins positioned on either side of an air cell and illustrating both the novel alignment and positioning of the fin louvers and representative paths of air particles passing therethrough;

FIGURE 4 is a partial view in perspective showing in spaced apant relationship the cutting and forming edges of the involute teeth of mating gear-like blades or die sections from each of two die rolls between which strip stock is passed tin accordance with this invention to form the vents and louvers of the fin proper and to initiate the folding of the fin strip between adjacent fins;

FIGURE 5 is an enlarged partial view in cross section of one embodiment of die rolls which may be used in the method of this invention showing in spaced apart relationship the alignment of teeth within each roll and with reference to the mating roll, and, in broken outline, representative displacement of strip stock by such teeth when in mesh;

FIGURE 6 is a reduced view in cross section of the die rolls taken at a angle to the view shown in FIGURE 5 with the terminal sections removed to show two intermediate cutting and forming blades of the type shown in FIGURE 4 in operating position upon a strip stock;

FIGURE 7 is a greatly enlarged view of a small portion of two mating blades similar to those shown in FIGURE 4 but differing in that when in mesh a slight interference is provided whereby the strip stock is compressed providing 3 controlled deformation at the midpoint between adjacent fins by the action of the corresponding tooth tip and root or clearance arc; and

FIGURE 8 is a cross sectional view taken along line 8--8 of FIGURE 7.

Referring to FIGURES 1-3, the radiator assembly, as will be readily understood, includes a heat dissipating unit or core 11, having at opposite ends a top tank or inlet header 12, and a bottom tank or outlet header 13, adapted for connection, respectively, with the discharge and intake conduits of a cylinder block cooling jacket. For the flow of cooling medium from one tank to the other the core is made up of a number of fluid passageways or water tubes 14, spaced apart by fin strips 15. The fin strip shown in the drawing is of folded or corrugated outline providing a series of fins 16 between folds or connecting members 17. The strips therefore extend between adjacent walls to the adjoining tubes to divide the space into a number of relatively small air cells or conduits 18. Ordinarily, the opposite edges or front and rear faces of the core assembly are dipped first in a flux and then in molten solder to seal the margins of the walls of the water tubes where necessary and to join the fin strips to the walls. If the passageways and fin strips are evenly formed so as to make possible continuous contacts from edge to edge, there will be an inward capillary fiow of solder toward the center of the core, and a positive bond will result throughout substantially the entire depth of the core to insure the free flow of heat into the fins.

Attention is now directed to the novel design of the fin proper and specifically to FIGURES 2 and 3 of the drawings. Fin 16 is planar, Le. a single plane can be passed simultaneously through the entire length of both the longitudinal and transverse axes. For purposes of convenience such plane is hereinafter referred to as the central plane or base plane.

Provided in the planar fin 16 are groups of parallel transverse slots 19, 24 and 26 through which air can pass from cell to cell. The slots 19 and the adjacent louvers are formed by slitting the planar fin and turning th interpositioned strips out of the central plane. Thus, in the embodiment shown the fin may be viewed as providing a pair of spaced apart louvered windows each of which provide a plurality of transverse openings between louvers which are aligned in parallel relationship with respect to the other louvers of the same window but inclined from the central plane of the fin at an equal and opposite angle from those of the next adjacent window. Although the fin of this embodiment provides only two of such windows it is to be understood that one or more additional windows may be provided in other embodiments with the same order of louver reversal with respect to adjacent windows.

The portion of the end supports adjacent the terminal slots 24 form outer diversion louvers 25 which are pivoted from their base so as to project outward from one side of the central or fin plane. The edges of central support 21 adjacent the central terminal slots 26 form inner or central diversion louvers 27. The term terminal herein is used with respect to a given window, i.e. grouping of louvers and hence may or may not mean terminal with respect to the entire fin. Louvers 27 are also pivoted from their base so as to project from the central plane on the side opposite louvers 25. It will be noted that each of the outer diversion louvers 25 is aligned in parallel relationship with the nearest inner or central diversion louver 27 and that louvers 25 and 27 extend from opposite sides of the central or fin plane. While the projecting edge of each of the outer diversion louvers 25 is inclined toward the nearest central support and in a two window fin toward the center thereof, the projecting edge of each of the inner or central diversion louvers 27 is inclined toward the nearest outer diversion louver or away from the center of the fin. The remainder of the fin provides a central support 21, positioned between such windows, side supports 22 and end supports 23.

The strips between slots 19 and between slots 19 and terminal slots 24 and 26 form intermediate louvers 28 each of which is turned out of the central plane by pivoting about its longitudinal axis so that louvers 28 extend out of the central plane in two opposing directions. However, it will be notedthat louvers 28 extend from the central plane for a lesser distance on each side of the central plane than do the diversion louvers extending from the corresponding side. In addition to being aligned .in parallel relationship with each other within each set, louvers 28 are also in parallel relationship with the diversion louvers 25 and 27 with which they are grouped.

Louvers 25, 27 and 28, except for the edges thereof where they are pivoted or twisted in relation to the supporting fin, are planar providing a smooth, flat surface along essentially their entire length and breadth. In this embodiment central support member 21 between inner diversion louvers 27 supported thereby is substantially equal in width to each of the louvers 27. The major transverse measurement of such louvers is preferably as small as the method of manufacture and requirements of structural strength will permit. Such louvers en masse therefore present to an air stream the largest practical wiping surface coupled with the minimum of impedance to air flow commensurate with maximum heat exchange efficiency.

The diversion louvers 25 and 27 as aforementioned extend farther from the central plane than intermediate louvers 28. Terminal slots 24 are also somewhat larger than intermediate slots 19. Slots 24, louvers 25, and louvers 27 being located in terminal and central positions are thus properly shaped, sized and positioned to provide a primary diversion effect upon an air stream entering one of the cells 18, escaping into an adjoining cell and eventually passing out of the radiator on the side opposite from whence it entered. In cooperation with slots 19 and louvers 28 the wiping air is passed along the louver faces from cell to cell until the path of a representative particle of air is directed into contact with central support 21 from whence -it is diverted by the inner diversion louver 27 that obstructs its original directional movement from cell to cell. This louver is aligned to divert the movement of the air particle toward a window of the adjoining fin opposite the window through which it passed before being diverted by louver 27 as illustrated in FIGURE 3.

This fin is thus designed to increase laminar flow and permits the contact of a greater amount of unheated and lightly heated air to a greater area of unclogged heat exchange surface per unit of time or per air unit pass. The term clogging here relates to the phenomenon whereby a heat exchange surface is blanketed by a clinging film of air.

In FIGURES 4-6 inclusive there is shown a novel device for making regularly spaced impressions on a sheet material that will maintain a defined shape after cutting and forming, e.g. suitable metals, plastics, etc. It should be understood at the outset that although the embodiment here shown is designed specifically to produce heat exchange fin structures of the type hereinbefore described, this invention can be adapted to produce an almost endless variety of fin strip designs and is equally adaptable to provide a wide variety of other articles from sheet metal I the production of which can be effected by the simultaneous cutting, forming, and shaping of repeated designs.

Referring now to FIGURE 4, there are shown a pair of gear-like cutting and forming blades 31 and 41 which have involute teeth 32 and 42 evenly spaced about their respective perimeters. In this view a cut-away portion of blade 41 is shown spaced apart from blade 31 of which only a portion of the perimeter is outlined in detail. Blades 31 and 41 are mounted on shafts 33 and 43 respective y.

Each of the teeth 32 and 42 provide two curved louverforming faces 34 and 44 respectively. Such faces on a given tooth are separated by a tip portion indicated by number 35 on blade 31. The curves described by each of the louver-forming faces 34 and 44 are involutes of a noncircular evolute and are further characterized in that they describe arcs of equal circles. One of the teeth 32 is shown in cross section to show both of the louver-forming faces. It should be understood that the distinction often made in gear terminology between the flank and the face of a tooth is not used in this specification and hence the curved faces 34 and 44 shall be understood to extend both inside and outside the pitch circle.

A broken line on one of the teeth 42 indicates the root circle 45. On the same tooth the locus of the points of intersection of the louver-forming faces 44 with the corresponding fillets 47 is indicated in broken line at 46. Farther up the same tooth the locus of the points of intersection of the louver-forming faces 44 with the corresponding tip arcs is indicated in broken line at 48.

The fillet 47 is the small curve connecting the tooth profile with the bottom of the tooth space in accordance with conventional gear terminology and the adjoining fillets of adjacent teeth form an arc 49 herein termed the root or clearance arc.

The louver-forming faces 34 and 44 viewed transversely each have a narrow cutting edge at one side. From this the remainder of the face slOpes inwardly =or recedes to the opposite edge. The shape of the louver-forming faces of the blades of this invention are best illustrated in FIG- URE 8 and will be more fully described in relation to that figure. As will be seen later in the description of FIGURE 5, this sloping surface and the corresponding surface of the mating tooth determines the angle at which the louver formed on a fin strip is inclined from the central plane of the fin. Thus, each of the involute louver-forming faces 34 and 44, for the greater part of its width, at any given point on the curve forms an acute angle with the transverse axis of the blade. Opposite portions of the two opposite louver-forming faces of a given tooth recede at equal rates. This pattern is repeated in the several teeth forming the perimeter of the blade.

For convenience of expression, the term working contact is used herein to describe the relationship of one blade rolling upon its mate with the thin strip of sheet stock positioned therebetween. Each involute face or surface is therefore adapted to mesh with and roll upon the mating faces of the mating blade, i.e. in edge-to-ed-ge working contact, and to maintain transverse line contact continuously from initiation of such contact between a given pair of mated faces until termination of the same.

The length, width and slope of the louver-forming surfaces 34 and 44 of the mating blades govern the size of the openings made in the sheet stock and the accompanying displacement of adjacent material. This displaced material becomes the louvers of the fin. The scissor-like cutting action requires a third surface in addition to the mating blades. This is ordinarily supplied by another blade in parallel relationship with the mating pair of blades as shown in FIGURE 5.

In FIGURE there is shown a portion of two gearlike die assemblies, i.e. cutting and forming rolls, and 40, made up from a plurality of plate-like, circular blades the majority of which are formed in like manner to the blades shown in FIGURE 4. The blades of each roll are mounted in parallel relationship upon a central shaft, not shown in FIGURE 5 but illustrated with the single blades in FIGURE 4. In this embodiment the blades employed are arranged in the manner necessary to produce the novel fin structures hereinbefore described. In FIGURE 5, the blades or gear wheels are shown in cross section to illustrate the transverse profile of the teeth and their mating relationship with the corresponding surface of the mating roll. In each such roll in this particular embodiment there are shown the terminal ends of eighteen angle faced or forming blades of the type described with reference to FIGURE 4 and the corresponding parts of three other gear wheels or flat faced blades the working surfaces of which are parallel to the transverse axis thereof.

In roll die 30 the working faces of sections '50, 60 and 70 are parallel to the transverse axis of their respective blades. Otherwise these sections or blades bear the same involute teeth as the blades hereinbefore described. Sections 150, 160 and 170 form the mating or corresponding parts of roll die 40. Terminal sections or gear wheels 50, 70, and 170 provide an ironing effect upon an external portion of the sheet stock adjacent the terminal louvers and form the neutral line for stock passing between such rolls. The formation of the slots and louvers hereinbefore described is carried out in two operational steps when rolls 30 and 40 are engaged in normal operating relationship and a strip of sheet stock is passed between the power driven rolls as illustrated in FIGURE 6. For example, the formation of one terminal louver is effected by the cooperative action of blades 51, 52 and 151. Before the corresponding parts of faces 91 and 92 of blades 51 and 151 can be rotated into contact with each other the leading or cutting edge 93 of blade 151 must pass in close parallel relationship with the leading edge 94 of blade 52 thereby shearing or cutting the sheet stock in a scissor-like action. Since this rolling working contact is made for the length of a given contact path of one side of a given tooth the cut made will be essentially the length of the path of contact, the involute. The continued movement which brings face 92 into rolling contact with face 91 along the entire path of working contact of the given louver-forming faces also presses that portion of the sheet stock in front of face 92 from the neutral line and against face 91 so as to assume the position shown in dotted line along face 91. The rolling action of faces 91 and 92 with strip material between them produces an ironing effect upon the resulting louver giving to the latter a smooth straight surface.

Adjoining louvers are formed by blades 52-59 and blades 152-159 inclusive but with the difference that the formation of each of these louvers involves making two cuts in the sheet material freeing the louver from support at two sides. The strip forming such louver is pivoted about its longitudinal axis to extend out of plane passing through the neutral line in two directions in contrast to the single displacement of the terminal or outer diversion louver, e.g. one side of a strip follows the cutting edge of blade 52 to the receding edge of 152 while the opposite side is pressed out of the neutral line by the cutting edge of 152 and comes to rest upon the receding edge of 52. Here again the rolling action provides an ironing effect upon the resulting louver. This novel effect is made possible because a line contact, transverse to the rotational axes of the mating blades, is maintained throughout the path of contact.

Centrally positioned blades 59, 61, 159 and 161 cooperate with center sections or gear wheels 60 and 160 in like manner to form a trough-like structure having center section and two dependent louvers as shown in FIGURES 2 and 3 and identified by numerals 21 and 27.

Blades 61-69 and 161-169 inclusive are in reverse alignment to blades 51-59 and 151-159 but operate in like manner providing louvers inclined in accordance with their alignment.

In FIGURE 6 a side view of die rolls 30 and 40 in operation position illustrates the crimping or pleating of a sheet metal stock 80 which also occurs as the latter is passed between the cutting and forming blades as hereinbefore described.

The fin forming operation initiates the folding of the fin strip between adjacent fins. Ordinarily this folding will be completed by a gathering device, not shown. Such devices are conventional tools in this art and do not comprise a part of this invention.

In the embodiment shown in FIGURES 4 through 6 inclusive, the rolls are spaced so that the clearance therebetween is essentially the same as the thickness of the sheet material being processed throughout the working contact path.

v A preferred embodiment is illustrated in FIGURE 7. In FIGURE 7 a small portion of the perimeters of blades 230 and 240 is shown greatly enlarged. Blades 230 and 240 have involute teeth 232 and 242 respectively. These teeth are provided With louver-forming involute faces 234 and 244 respectively. Both blades have tooth tips 235 and root or clearance arcs 249. However, the blades in this embodiment are designed to provide a slight clearance interference in that the shortest distance between the high point or transverse bisector 236 of tips 235 and the low point or transverse bisector 251 of root arcs 249 is slightly less than the clearance between the involute louver-forming faces 234 and 244 and slightly less than the thickness of the strip stock. Thus, in one embodiment where the thickness of the strip stock is .003 inch the clearance between the louver-forming faces is .003 inch while the shortest distance between the fold-forming tip and root arc combination is about .0025 inch. This causes a slight compression and deformation of the strip stock at the bend between fins and provides a particularly effective fold.

The cross sectional view in FIGURE 8 is also enlarged to better illustrate the shape of the louver-forming faces 234 and 244. Here, these involute faces clearly show cutting edges 253 and 255 respectively which are parallel with the transverse axis of their respective blades and sloped forming edges 257 and 259 respectively which form an acute angle with the same.

It is to be seen that such device provides a novel ironing effect made possible by the involute shape of the louver-forming surfaces and the cooperative action of the tooth tips with the surfaces of the root arcs. This not only provides smooth regular surfaces on the finished product in general but also makes possible the formation of straight or planar louvers, i.e. louvers which except for their twisted ends are fiat sheets.

A method for designing and manufacturing a roll die of the type hereinbefore described and illustrated in the accompanying drawings is described in detail in U.S. Patent 3,214,954, aforementioned.

Having thus described the invention with particularity, it is obvious that modifications can be made in the same without departing from the spirit and scope of the invention as set forth in the appended claims.

We claim:

1. Ina method of manufacturing a heat exchange element from a strip of sheet metal which comprises passing said strip between a first roll die and a second roll die, folding said strip to form therein a plurality of evenly spaced fin elements each having an essentially planar base, simultaneously cutting a plurality of slits within each of said fin elements parallel to each other and to the longitudinal axis of said strip and simultaneously turning strips of metal between adjacent members of said slits out of the plane of said planar base to form louvers, the improvement which comprises providing on opposite sides of said fin elements while said slits are cut and said strips are turned, opposing line pressures extending transversely in relation to said strip of metal.

2. The method of claim 1 wherein said opposing line pressures extend transversely in relation to said strip of sheet metal, longitudinally in relation to said planar base, and between the terminal louvers of each of said fin elements. 4

3. The method of claim 1 wherein said opposing line pressures extend transversely in relation to said strip of sheet metal and through the points of cutting.

4. The method of claim 1 wherein said opposing line pressures extend transversely in relationship to said strip of sheet metal, longitudinally in relation to said planar base and between said slits in line with the points of cutting.

References Cited JOHN F. CAMPBELL, Primary Examiner.

D. C. REILEY, Assistant Examiner.

U.S. Cl. X.R. 29157.3; 72-326 

